1. Field of the Invention
This invention pertains to card housings for printed circuit boards, and more specifically, to card housings having an insulative cover and ground feature that facilitates and enhances the ability to manufacture and assemble card housings.
2. Discussion of the Background
Cards encasing printed circuit boards ("PCB"), generally referred to as "PC cards", are widely employed devices that expand the versatility and capacity of computer processing units, most notably in laptop and palm sized computers. Examples of PC cards include memory cards, which serve to expand or diversify the memory capacity of the CPU. Still, other types of PC cards enhance the I/O functions of the CPU by providing communication capabilities for fax-modems and peripheral devices.
Industry standards for promoting uniform specification and design of some PC cards is promulgated by the Personal Computer Card International Association (PCMCIA), and alternatively, in Japan by the Japan Electronic Industry Development Association (JEIDA). PCMCIA cards are commonly differentiated into three formats known as Type I, II, or III. All three formats have identical rectangular dimensions, but differ in the respective thickness. Type I cards have a uniform thickness of 3.3 mm, Type II cards are approximately 5.0 mm thick with 3.3 mm thick edges, and Type III cards are approximately 10.5 mm thick with 3.3 mm thick outside edges. Still, other types of PC cards exist, including Compact Flash cards and miniature cards, as manufactured and employed by the Intel Corporation and others.
In basic form, PC cards are rectangular, with lateral sides and a front end and a back end, and comprise a pair of opposing metallic covers and a plastic frame surrounding a printed circuit board. The metallic covers are usually stamped to conform to the desired specifications. As practiced in the art, the plastic frame is injection molded to each cover, and the two halves are joined to form the whole PC card. The printed circuit board is formed from a planar substrate having one or more electrical components mounted to either side. The front end of the PC card is generally designated to mate with the host computer. For PCMCIA cards, the host connector is female and provides for 68 pins. The back end may provide for switches, I/O connectors, extensions providing I/O connectors, RJ plug receivers, or other features.
One feature generally included in PC cards is a ground element that acts as a circuit ground for the circuit board engaged with the host or peripheral connector. The ground element may also be required to provide a chassis ground for remedying the build up of electrostatic charge and electromagnetic interference inherently created by the electrical components contained within the card. The prior art provides several designs for PC cards that employ various ground elements. In particular, U.S. Pat. No. 5,187,642 to Garner et al. discloses metal rails that attach to the integrated circuit substrates on both lateral sides of the circuit boards. U.S. Pat. No. 4,725,920 to Ijichi et al. discloses a separate grounding plate sandwiched between two printed circuit substrates. U.S. Pat. No. 5,749,741 to Bellas et al. provides for grounding clips that are mounted to, or otherwise electrically connected to, a terminal that is mated with the planar substrate. These and other references not mentioned herein provide for the grounding element as an extra component interconnected to the PC card.
The increased demand for PC cards has created the need for simpler and more efficient incorporation of a ground element within the PC card. A more efficient method of providing a ground element is to employ the two stamped metallic covers as a grounding feature of the PC card, as disclosed by U.S. Pat. No. 5,544,007 to Inoue. Inoue provides alternative grounding elements, including conductive portions that extends from each stamped cover to contact one another when the covers are joined, where the conductive elements combine with a ground spring between the substrate and the cover to ground the whole PC card. However, Inoue requires that the stamped covers be formed entirely of conductive material.
The modular appeal of PC cards and their widespread popularity has created the need for PC cards having customized features that enhance physical and aesthetic characteristics of the PC card. For example, color-coded covers may be employed to designate a particular function or manufacturer of the PC card. According to the related art, coloring or designing the external surface of the PC card is preferably accomplished by way of insulative coats made of plastic or paint. In addition, PC card housings may be customized to provide a particular external tactile surface, or to provide for an external insulative plastic coating. Such external customizations generally must be incorporated into the PC card housing in one of two ways. First, the covers may be formed from insulative material, with an extra grounding member contained therein that is isolated from the stamped covers. However, the additional ground feature is an additional feature that must be integrated between the housing and the printed circuit board, thereby adding manufacturing and labor cost to the overall cost. Second, and alternatively, the grounding element may be stamped with the covers, and an additional decorative insulative coat may be applied to the exterior of the PC card housing as an additional step. Post-assembly application of decorative insulative coats to the covers is also costly, and requires additional equipment and manufacturing capabilities.
It is therefore an object of the invention to provide for a PC card having stamped metal covers with a grounding element unitarily incorporated therein.
Another object of the invention is to provide a ground feature on a PC card housing that acts as a circuit ground and/or a chassis ground.
Still another object of the invention is to provide a PC card manufactured by pre-customized stamped metal covers, each of which provide a customized external surface.